Using undercoat on bare wood?

[zenonithus]

Hey all, So I did that thing again where I do an entire room and then read I done it wrong

I stripped all the paint from the wood skirting and door frame and applied two coats of water based white undercoat to the wood. Now I'm reading that it first needs to have primer before the undercoat? I definitely cannot strip this wood again, it was a nightmare the first time! Is the undercoat on just the bare wood ok? Will it peel off or something? Seems pretty good to me though haven't tested if it scratches off easily. I was planning to then give two coats of satin white on top of that.

 

[Nige F]

What make of paint ?

 

[zenonithus]

its Wikes trade undercoat

 

[Doggit]

There's several, is it acrylic. Either way, you should be able to use 2 coats of acrylic primer/undercoat, and then use a water based topcoat.

 

[chappers]

should be fine

 

[zenonithus]

cheers guys, yeah watching all these YouTube vids they talk about applying primer first then undercoat then finish paint. Though is primer and undercoat more or less the same thing?

 

[Doggit]

No, the primer seals the wood, and stops the paint soaking into it, and an undercoat provides a good key for the topcoat. But there are a lot of primer undercoats nowadays that do a dual job, but then require 2 coats instead.

 

[zenonithus]

Yeah this undercoat seems very thick and fills in gaps and holes, hopefully its the primer type. Does the primer undercoat need to be 100% opaque? Or will two top coats of finish be enough?

 

[Chud]

Yeah this undercoat seems very thick and fills in gaps and holes, hopefully its the primer type. Does the primer undercoat need to be 100% opaque? Or will two top coats of finish be enough?

IMO it should be Opaque - are you seeing the colour of the wood through it? N.B. if you're seeing knots then you may need to apply a stainblocker in those places - zinnser is good stuff but for quick spot blocking I've found the no nonsense aerosol from screwfix to be very good.

 

[zenonithus]

I've given the picture rail two coats. It's pretty white but there is still a hint of wood. Do you think it's worth giving another coat for just the picture rail?

 

[Chri5]

I've given the picture rail two coats. It's pretty white but there is still a hint of wood. Do you think it's worth giving another coat for just the picture rail?

Do you? (Its your eyes that will see it).

 

[Chri5]

No, the primer seals the wood, and stops the paint soaking into it, and an undercoat provides a good key for the topcoat. But there are a lot of primer undercoats nowadays that do a dual job, but then require 2 coats instead.

Sorry to seem like a nerd, but your not saying it how I would.

Primer is thinner than undercoat, primer acts as a sealer / bonder between wood and undercoat.

It doesn't sit on the wood it penetrates, undercoat doesn't penetrate wood (anywhere near as much as a primer will).

OP- you should note that most decent water base satin finishes can act as an undercoat. Check the spec of yours, and in future always prime bare wood, hopefully you stopped the knots, otherwise you may get bleeding through the finish when sap seeps from the knots due to room temp curing wood (more than a wood yard does).

 

[zenonithus]

its pretty old wood from the 1920s. With the knots you mean make sure they are sealed in paint? If it is just undercoat on the wood will there be issues with the bonding in future? Will the paint crack or something?

 

[chappers]

As I said it should be OK very much doubt it will peel off, but keep undercoating until the colour is flat over the whole thing before top coating.
My process for bare wood would be;

Knotting over knots- probably not necessary for old stripped wood
1 coat primer, 2 coats undercoat- de-nibbed with 250-300 grit paper after each coat
2 coats top coat- keyed with 400 grit between coats if more than 24 hours between coats

 

[Gerrydelasel]

For future reference:
http://www.thejoyofmoldings.com/quick-tip-the-unifying-coat-of-primer/